Modern light emitting diode (LED) displays increasingly use optical systems at the front of the display in order to increase optical performance characteristics, such as contrast ratio, brightness, viewing angle, colour compound.
One of the most frequently used devices for increased optical performance, is the shading device. A shader for LED displays generally consists of a grid which fits over the LEDs and fills up the space between the LEDs. The shading device can have several optical features like louvers for avoidance of angled direct light hitting the front of the LED. Other optical features embedded in the shading device are light-traps which consist of cavities which are dimensioned in such a way that incoming light is caught in these cavities, yielding better contrast for the display.
One of the main problems with shaders is the way to attach them to the LED printed circuit board (PCB). Usually the shader is glued to the LED PCB, leading to difficulty to remove if any repair work needs to be done to the LEDs or the LED PCB. Ideal is a removable shader. A removable shading device is convenient however very difficult to manufacture. Major problem is that the shading device must be firmly connected to the front of the LED PCB. This is often done by a number of extending clips which are standing orthogonally on the back of the shading device. These clips are very vulnerable to breaking and moreover with very small pitch (e.g. 4 mm) clips are almost impossible to add to the shader mechanics. Because of the difficulty to add clips, only a few of them are usually added which results in very bad and irregular mechanical fitting of the shading device to the LED PCB. This irregular fitting results in uneven mechanical fitting of the shader, overall on the front of the display, which finally causes a non uniform display. So with this technique a few hard connections (clips) hold the shader to the LED PCB.